1. Field of the Invention
The present invention relates to an electromagnetic induction-type conductivity meter for measuring a conductivity of a sample liquid, such as a solution, utilizing an electromagnetic induction current.
2. Description of Related Art
Conductivity meters have been used to analyze properties of liquid samples. FIG. 4(A) schematically shows a construction of a measuring portion of a conventional electromagnetic induction-type conductivity meter. A housing or case 31 is made of a resin material and is provided with a liquid-flowing passageway 37 consisting of a vertical passageway 33 having an opening 32 at its lower end portion and a horizontal passageway 36 having openings 34, 35 on its (right and left) sides for communicating with the vertical passageway 33. A transformer chamber 40 encloses an exciting transformer 38 and a detecting transformer 39 therein under the condition that they are insulated from each other and formed at one end of the housing 31.
The transformers 38 and 39 are of the same size and their respective iron cores 41, 42 are circular. An exciting coil 43 and a detecting coil 44 are wound around, respectively, iron core 41 and iron core 42. The vertical passageway 33 is arranged so as to pass through the 11 respective centers of the iron cores 41, 42 of both transformers 38, 39.
In an electromagnetic induction-type conductivity meter having the above-described construction, if an alternating voltage having an appointed magnitude and an appointed frequency is applied between the terminals of exciting coil 43 of the exciting transformer 38 under a condition wherein the measuring portion is immersed in a liquid to be measured such as a solution, the liquid to be measured passing through the passageway 33 acts as a one turn coil, whereby an alternating current, i.sub.c, resulting from an electromagnetic induction will flow, as shown in FIG. 4(B). Thus, an alternating electromotive force can be induced between the terminals of the detecting coil 44 of the detecting transformer 39. This alternating electromotive force is equal to the alternating voltage applied to the exciting coil 43 in frequency, and its magnitude is proportional to an electrical conductivity of the sample liquid to be measured as it flows through the liquid-flowing passageway 37. Accordingly, the electrical conductivity of the liquid to be measured can be measured by using a calibration liquid, such as an aqueous solution of KCI having an appointed concentration, to preliminarily establish a graph showing a relationship between the alternating electromotive force (mV) and the electrical conductivity (mS/cm) of the calibration liquid.
However, in an electromagnetic induction-type conductivity meter of this type, its detecting sensitivity can be reduced over a period of use, so that it is necessary to periodically check the detecting sensitivity. Accordingly, conventionally, a measurement of electrical conductivity of a sample liquid to be measured must be interrupted to remove the measuring portion from the sample liquid to be measured and to immerse the measuring portion in a calibration liquid, such as an aqueous solution of KCI having an appointed concentration, thereby periodically checking the detecting sensitivity of the instrument.
According to the above-described calibrating method, disadvantages have occurred in that a measurement of the electrical conductivity of a sample liquid to be measured must be interrupted for calibration. If the measuring portion with the calibration liquid adhering to a surface thereof is subsequently immersed in the sample liquid to be measured as it is, the liquid to be measured is contaminated with the calibration liquid.
Thus, the industry is still seeking to simplify and improve the accuracy and use of conductivity meters.